Method of manufacturing semiconductor device

ABSTRACT

Exposure of a gate conductive film covered by an interlayer insulation film in a unit cell portion is reduced when a gate contact region is formed. A method of manufacturing a semiconductor device includes forming a gate conductive film to come in contact with a gate oxide film in a unit cell portion, forming a gate wire to come in contact with the gate oxide film in a termination region, forming a first insulation film on an upper surface of the gate wire in the termination region, subjecting an upper surface of the gate conductive film in the unit cell portion to thermal oxidation with use of the first insulation film as a mask to form a thermal oxide film on the upper surface of the gate conductive film, and forming a second insulation film covering the first insulation film and the thermal oxide film.

TECHNICAL FIELD

A technology disclosed in the specification of the present application relates to a SiC-MOSFET including a structure for reducing a leak failure between a gate and a source, for example.

BACKGROUND ART

A manufacturing process of a SiC-metal-oxide-semiconductor field-effect transistor (MOSFET) in a case of using silicon carbide as a semiconductor will be described below.

First, in a unit cell portion, an n-type source implantation region is formed on a surface layer of a p-type well implantation region. Then, a gate oxide film is formed at least on an upper surface of the p-type well implantation region sandwiched between the n-type source implantation region and an n-type epitaxial layer.

Meanwhile, in a termination region, a field oxide film is formed on an upper surface of the p-type well implantation region. Then, a gate oxide film is formed on an upper surface of the field oxide film.

Then, in the unit cell portion, a gate conductive film made of polysilicon or the like is patterned to be formed on an upper surface of the gate oxide film. Further, in the termination region, a gate wire for making a contact with the gate conductive film and a front-surface electrode to be described later in the unit cell portion of the transistor is patterned to be formed on the upper surface of the gate oxide film.

After that, in the unit cell portion, an entire upper surface of the gate conductive film is subjected to cap oxidation to form a thermal oxide film. Then, a CVD oxide film, which is formed with a chemical vapor deposition (CVD) method, covering an upper surface of the thermal oxide film and a side surface of the gate conductive film is formed.

Meanwhile, in the termination region, an upper surface of the gate wire is oxidized to form a thermal oxide film. Then, a CVD oxide film covering an upper surface of the thermal oxide film and a side surface of the gate wire is formed.

Here, in the unit cell portion, the thermal oxide film formed to cover the gate conductive film and the CVD oxide film covering the upper surface of the thermal oxide film and the side surface of the gate conductive film are collectively referred to as an interlayer insulation film in the unit cell portion. A film thickness of the interlayer insulation film in the unit cell portion on the upper surface of the gate conductive film is a thickness obtained by adding together a film thickness of the thermal oxide film and a film thickness of the CVD oxide film.

Further, in the termination region, the thermal oxide film formed to cover the gate wire and the CVD oxide film covering the upper surface of the thermal oxide film and the side surface of the gate wire are collectively referred to as an interlayer insulation film in the termination region. A film thickness of the interlayer insulation film in the termination region on the upper surface of the gate wire is a thickness obtained by adding together a film thickness of the thermal oxide film and a film thickness of the CVD oxide film.

Next, in the unit cell portion, a source contact is opened in the CVD oxide film. Then, in order to reduce contact resistance, a silicide is formed in the source contact region. Further, in the termination region, a gate contact is opened in the interlayer insulation film.

Next, the front-surface electrode covering the source contact region and the gate contact region is formed.

Here, to make an ohmic contact with a silicide of Ni and SiC, i.e., NiSi, high temperature annealing of approximately 1000° C. needs to be performed after depositing Ni.

However, when the silicide is formed in the source contact region in the unit cell portion while the gate contact region is formed in the termination region, the gate wire made of polysilicon or the like in the termination region may abnormally grow due to reaction with Ni at a high temperature of approximately 1000° C. In such a case, polysilicon of the gate wire in the termination region is eliminated.

Accordingly, when the silicide is formed in the source contact region, the interlayer insulation film in the termination region needs to be reserved without forming the gate contact region such that a silicide is not formed in the gate contact region.

Therefore, in the manufacturing process of the SiC-MOSFET, for example, as illustrated in Patent Document 1, first, only the source contact region is opened in the unit cell portion to form a silicide in the region, and then the gate contact region is formed.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent Application Laid-Open No. 2014-150279

SUMMARY Problem to be Solved by the Invention

In the above-mentioned SiC-MOSFET structure, the film thickness of the interlayer insulation film in the unit cell portion and the film thickness of the interlayer insulation film in the termination region are equal. Therefore, for example, if a swelling locally occurs in the interlayer insulation film in the unit cell portion due to presence of a defect caused by a foreign matter or the like on an upper surface of the interlayer insulation film in the unit cell portion or due to presence of a defect caused by a foreign matter or the like on a lower surface of the interlayer insulation film in the unit cell portion, when the gate contact region is patterned with use of a resist, a portion where the swelling of the interlayer insulation film in the unit cell portion occurs cannot be normally covered by the resist.

In such a case, when the gate contact region is etched to be formed, the interlayer insulation film in the unit cell portion not covered by the resist may also be etched. Then, when the interlayer insulation film in the unit cell portion is etched to cause the gate conductive film to be exposed at an unintentional portion, a leak failure between a gate and a source may occur.

The technology disclosed in the specification of the present application has been achieved in order to solve the problems as described above, and relates to a technology of reducing exposure of a gate conductive film covered by an interlayer insulation film in a unit cell portion even when a swelling locally occurs in the interlayer insulation film in the unit cell portion when a gate contact region is formed.

Means to Solve the Problem

A first aspect of a technology disclosed in the specification of the present application includes forming a gate oxide film on an upper surface of a semiconductor layer, forming a gate conductive film to come in contact with the gate oxide film in a unit cell portion, forming a gate wire to come in contact with the gate oxide film in a termination region provided to surround the unit cell portion in plan view, forming a first insulation film on an upper surface of the gate wire in the termination region, subjecting an upper surface of the gate conductive film in the unit cell portion to thermal oxidation with use of the first insulation film as a mask to form a thermal oxide film on the upper surface of the gate conductive film, and forming a second insulation film covering the first insulation film and the thermal oxide film.

Effects of the Invention

The first aspect of the technology disclosed in the specification of the present application includes forming a gate oxide film on an upper surface of a semiconductor layer, forming a gate conductive film to come in contact with the gate oxide film in a unit cell portion, forming a gate wire to come in contact with the gate oxide film in a termination region provided to surround the unit cell portion in plan view, forming a first insulation film on an upper surface of the gate wire in the termination region, subjecting an upper surface of the gate conductive film in the unit cell portion to thermal oxidation with use of the first insulation film as a mask to form a thermal oxide film on the upper surface of the gate conductive film, and forming a second insulation film covering the first insulation film and the thermal oxide film. According to such a configuration, when a gate contact region is formed, exposure of the gate conductive film covered by the interlayer insulation film in the unit cell portion can be reduced even when a swelling locally occurs in the interlayer insulation film in the unit cell portion.

These and other objects, features, aspects and advantages of the technology disclosed in the specification of the present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view schematically illustrating a structure of a metal-oxide-semiconductor field-effect transistor according to an embodiment.

FIG. 2 is a cross-sectional view schematically illustrating a cross-sectional structure of a unit cell portion of the transistor according to the embodiment.

FIG. 3 is a cross-sectional view schematically illustrating a cross-sectional structure of a termination region according to the embodiment.

FIG. 4 is a cross-sectional view schematically illustrating a cross-sectional structure of the unit cell portion according to the embodiment.

FIG. 5 is a cross-sectional view schematically illustrating a cross-sectional structure of the termination region according to the embodiment.

FIG. 6 is a cross-sectional view schematically illustrating a cross-sectional structure of the termination region according to the embodiment.

FIG. 7 is a cross-sectional view schematically illustrating a cross-sectional structure of the unit cell portion according to the embodiment.

FIG. 8 is a cross-sectional view schematically illustrating a cross-sectional structure of the termination region according to the embodiment.

FIG. 9 is a cross-sectional view schematically illustrating a cross-sectional structure of the unit cell portion according to the embodiment.

FIG. 10 is a cross-sectional view schematically illustrating a cross-sectional structure of the unit cell portion according to the embodiment.

FIG. 11 is a cross-sectional view schematically illustrating a cross-sectional structure of the termination region according to the embodiment.

DESCRIPTION OF EMBODIMENT

An embodiment will be described below with reference to the attached drawings.

Note that the drawings are schematically illustrated, and for the sake of description, a configuration is omitted or a configuration is simplified as appropriate. Further, an interrelationship of a size and a position of a configuration etc. illustrated in each different drawing is not necessarily accurately illustrated, and may be changed as appropriate.

Further, in the description below, similar components are denoted by the same reference symbols, and a term and a function of such components are similarly regarded. Accordingly, detailed description of such components may be omitted to avoid redundancy.

Further, in the description below, even when terms signifying a specific position and a direction, such as “up,” “down,” “left,” “right,” “side,” “bottom,” “front,” or “back,” may be used, these terms are used for the sake of convenience to facilitate understanding of the details of the embodiment, and are not related to directions in a case of actual implementation.

Further, in the description below, even when ordinal numbers, such as “first” or “second,” may be used, these terms are used for the sake of convenience to facilitate understanding of the details of the embodiment, and the order etc. that may be defined by these ordinal numbers are not restrictive.

Embodiment

Now, a method of manufacturing a semiconductor device according to the embodiment is described. For the sake of description, first, a structure of a MOSFET is described.

FIG. 1 is a plan view schematically illustrating a structure of a metal-oxide-semiconductor field-effect transistor including a unit cell portion 11 and a termination region 12. Further, FIG. 2 is a cross-sectional view schematically illustrating a cross-sectional structure of the unit cell portion 11 of the transistor. Further, FIG. 3 is a cross-sectional view schematically illustrating a cross-sectional structure of the termination region 12, which is formed to surround the unit cell portion 11 in plan view.

A manufacturing process of a case in which the transistor illustrated in FIG. 1, FIG. 2, and FIG. 3 is a SiC-MOSFET using silicon carbide as a semiconductor will be described below with reference to FIG. 1, FIG. 2, and FIG. 3.

First, in the unit cell portion 11 and the termination region 12, an n-type epitaxial layer 25 is epitaxially grown on an upper surface of an n-type SiC semiconductor substrate 26. Next, a p-type well implantation region 24 is formed on a surface layer of the epitaxial layer 25.

Next, in the unit cell portion 11, an n-type source implantation region 23 is formed on a surface layer of the p-type well implantation region 24. Then, a gate oxide film 21 is formed at least on an upper surface of the p-type well implantation region 24 sandwiched between the n-type source implantation region 23 and the n-type epitaxial layer 25.

Meanwhile, in the termination region 12, a field oxide film 29 is formed on an upper surface of the p-type well implantation region 24. Then, a gate oxide film 21 is formed on an upper surface of the field oxide film 29.

Then, in the unit cell portion 11, a gate conductive film 2 a made of polysilicon or the like is patterned to be formed on an upper surface of the gate oxide film 21. Further, in the termination region 12, a gate wire 3 a for making a contact with the gate conductive film 2 a and a front-surface electrode 28 to be described later in the unit cell portion 11 of the transistor is patterned to be formed on the upper surface of the gate oxide film 21.

Note that a back-surface electrode 27 is formed on a lower surface of the n-type SiC semiconductor substrate 26.

After that, in the unit cell portion 11, an entire upper surface of the gate conductive film 2 a is subjected to cap oxidation to form a thermal oxide film 2 d. Then, a CVD oxide film 2 b covering an upper surface of the thermal oxide film 2 d and a side surface of the gate conductive film 2 a is formed.

Meanwhile, in the termination region 12, in the above-mentioned process, an upper surface of the gate wire 3 a is oxidized to form a thermal oxide film 3 d. Then, a CVD oxide film 3 b covering an upper surface of the thermal oxide film 3 d and a side surface of the gate wire 3 a is formed.

Here, in the unit cell portion 11, the thermal oxide film 2 d formed to cover the gate conductive film 2 a and the CVD oxide film 2 b covering the upper surface of the thermal oxide film 2 d and the side surface of the gate conductive film 2 a are collectively referred to as an interlayer insulation film 200. A film thickness of the interlayer insulation film 200 on the upper surface of the gate conductive film 2 a is a thickness obtained by adding together a film thickness of the thermal oxide film 2 d and a film thickness of the CVD oxide film 2 b.

Further, in the termination region 12, the thermal oxide film 3 d formed to cover the gate wire 3 a and the CVD oxide film 3 b covering the upper surface of the thermal oxide film 3 d and the side surface of the gate wire 3 a are collectively referred to as an interlayer insulation film 300. A film thickness of the interlayer insulation film 300 on the upper surface of the gate wire 3 a is a thickness obtained by adding together a film thickness of the thermal oxide film 3 d and a film thickness of the CVD oxide film 3 b.

Next, in the unit cell portion 11, a source contact is opened in the CVD oxide film 2 b. Specifically, the CVD oxide film 2 b and the gate oxide film 21 are etched to form a source contact region 100. Then, in order to reduce contact resistance, a silicide 22 is formed in the source contact region 100. Note that FIG. 2 illustrates a state in which the source contact region 100 is formed in a manner described above, and the silicide 22 is formed in the source contact region 100.

Further, in the termination region 12, a gate contact is opened in the interlayer insulation film 300. Specifically, the CVD oxide film 3 b and the thermal oxide film 3 d are etched to form a gate contact region 3 c. Note that FIG. 3 illustrates a state in which the gate contact region 3 c is formed in a manner described above.

Next, the front-surface electrode 28 covering the source contact region 100 and the gate contact region 3 c is formed.

Here, to make an ohmic contact with a silicide of Ni and SiC, i.e., NiSi, high temperature annealing of approximately 1000° C. needs to be performed after depositing Ni.

However, when the silicide 22 is formed in the source contact region 100 in the unit cell portion 11 while the gate contact region 3 c is formed in the termination region 12, the gate wire 3 a made of polysilicon or the like in the termination region 12 may abnormally grow due to reaction with Ni at a high temperature of approximately 1000° C. In such a case, polysilicon of the gate wire 3 a is eliminated.

Accordingly, when the silicide 22 is formed in the source contact region 100, the interlayer insulation film 300 needs to be reserved without forming the gate contact region 3 c such that a silicide is not formed in the gate contact region 3 c.

Here, in the above-mentioned SiC-MOSFET structure, a film thickness of the interlayer insulation film 200 and a film thickness of the interlayer insulation film 300 are equal. Therefore, for example, if a swelling locally occurs in the interlayer insulation film 200 due to presence of a defect caused by a foreign matter or the like on an upper surface of the interlayer insulation film 200 or due to presence of a defect caused by a foreign matter or the like on a lower surface of the interlayer insulation film 200, when the gate contact region 3 c is patterned with use of a resist, a portion where the swelling of the interlayer insulation film 200 occurs cannot be normally covered by the resist.

In such a case, when the gate contact region 3 c is etched to be formed, the interlayer insulation film 200 in the unit cell portion 11 not covered by the resist may also be etched. Then, when the interlayer insulation film 200 is etched to cause the gate conductive film 2 a to be exposed at an unintentional portion, a leak failure between a gate and a source may occur.

Manufacturing Process of Method of Manufacturing Semiconductor Device

A method of manufacturing the SiC-MOSFET according to the embodiment will be described below. Here, FIG. 4 is a cross-sectional view schematically illustrating a cross-sectional structure of the unit cell portion according to the embodiment. Further, FIG. 5 is a cross-sectional view schematically illustrating a cross-sectional structure of the termination region according to the embodiment.

First, an n-type epitaxial layer 25 is epitaxially grown on an upper surface of an n-type SiC semiconductor substrate 26. Next, a p-type well implantation region 24 is formed on a surface layer of the epitaxial layer 25.

Next, in the unit cell portion 11, an n-type source implantation region 23 is formed on a surface layer of the p-type well implantation region 24. Then, a gate oxide film 21 is formed at least on an upper surface of the p-type well implantation region 24 sandwiched between the n-type source implantation region 23 and the n-type epitaxial layer 25.

Meanwhile, in the termination region 12, a field oxide film 29 is formed on an upper surface of the p-type well implantation region 24. Then, a gate oxide film 21 is formed on an upper surface of the field oxide film 29.

Then, in the unit cell portion 11, a gate conductive film 2 a made of polysilicon or the like is patterned to be formed on an upper surface of the gate oxide film 21. Further, in the termination region 12, a gate wire 3 a for making a contact with the gate conductive film 2 a and a front-surface electrode 28 to be described later in the unit cell portion 11 of the transistor is patterned to be formed on the upper surface of the gate oxide film 21.

Note that a back-surface electrode 27 is formed on a lower surface of the n-type SiC semiconductor substrate 26.

Next, in the unit cell portion 11 and the termination region 12, for example, an insulation film being a silicon nitride film is formed. Then, etching is performed such that the insulation film is reserved only on an upper surface of the gate wire 3 a in the termination region 12, to form an insulation film 103 d.

Here, FIG. 6 is a cross-sectional view schematically illustrating a cross-sectional structure of the termination region according to the embodiment. In FIG. 6, the insulation film 103 d is formed only on the upper surface of the gate wire 3 a.

Next, with use of the insulation film 103 d formed in the termination region 12 as a protective film, i.e., as a mask, in the unit cell portion 11, an upper surface of the gate conductive film 2 a is subjected to cap oxidation, i.e., thermal oxidation. In such a manner, a thermal oxide film 102 d is formed on the upper surface of the gate conductive film 2 a. In this case, the insulation film 103 d serves as a protective film of cap oxidation in the termination region 12, and therefore polysilicon of the gate wire 3 a in the termination region 12 is not oxidized.

Here, FIG. 7 is a cross-sectional view schematically illustrating a cross-sectional structure of the unit cell portion according to the embodiment. In FIG. 7, the thermal oxide film 102 d is formed on the upper surface of the gate conductive film 2 a.

Next, in the unit cell portion 11 and the termination region 12, a CVD oxide film is formed. Specifically, in the unit cell portion 11, a CVD oxide film 102 b covering an upper surface of the thermal oxide film 102 d and a side surface of the gate conductive film 2 a is formed. Note that the oxide film may be an oxide film formed with another method.

Further, in the termination region 12, a CVD oxide film 103 b covering an upper surface of the insulation film 103 d and a side surface of the gate wire 3 a is formed. Note that the oxide film may be an oxide film formed with another method.

Here, FIG. 8 is a cross-sectional view schematically illustrating a cross-sectional structure of the termination region according to the embodiment. In FIG. 8, the CVD oxide film 103 b covering the upper surface of the insulation film 103 d and the side surface of the gate wire 3 a is formed.

Here, in the unit cell portion 11, the thermal oxide film 102 d formed to cover the gate conductive film 2 a and the CVD oxide film 102 b covering the upper surface of the thermal oxide film 102 d and the side surface of the gate conductive film 2 a are collectively referred to as an interlayer insulation film 200A. A film thickness of the interlayer insulation film 200A on the upper surface of the gate conductive film 2 a is a thickness obtained by adding together a film thickness of the thermal oxide film 102 d and a film thickness of the CVD oxide film 102 b.

Further, in the termination region 12, the insulation film 103 d formed to cover the gate wire 3 a and the CVD oxide film 103 b covering the upper surface of the insulation film 103 d and the side surface of the gate wire 3 a are collectively referred to as an interlayer insulation film 300A. A film thickness of the interlayer insulation film 300A on the upper surface of the gate wire 3 a is a thickness obtained by adding together a film thickness of the insulation film 103 d and a film thickness of the CVD oxide film 103 b.

As described above, the insulation film 103 d and the thermal oxide film 102 d are formed through different processes. Accordingly, the film thickness of the thermal oxide film 102 d in the unit cell portion 11 can be increased to be larger than the film thickness of the insulation film 103 d in the termination region 12 by adjusting each forming condition, such as forming time.

Next, in the unit cell portion 11, the CVD oxide film 102 b and the gate oxide film 21 are etched to form a source contact region 100. The source contact region 100 exposes the source implantation region 23. Here, FIG. 9 is a cross-sectional view schematically illustrating a cross-sectional structure of the unit cell portion according to the embodiment. In FIG. 9, the source contact region 100 is formed in the CVD oxide film 102 b.

Then, in order to reduce contact resistance, a silicide 22 is formed in the source contact region 100. Here, FIG. 10 is a cross-sectional view schematically illustrating a cross-sectional structure of the unit cell portion according to the embodiment. In FIG. 10, the silicide 22 is formed in the source contact region 100. In this case, a gate contact in the termination region 12 is not opened, and therefore the gate wire 3 a made of polysilicon or the like does not react with Ni at a high temperature.

Next, in the termination region 12, a gate contact is opened in the interlayer insulation film 300A. Specifically, the CVD oxide film 103 b is etched with use of a resist mask, and the insulation film 103 d is etched with use of the same resist mask, to form a gate contact region 3 c. The gate contact region 3 c exposes the gate wire 3 a.

Here, the insulation film 103 d is made of a type of a material different from that of the CVD oxide film 102 b, the thermal oxide film 102 d, and the CVD oxide film 103 b. Therefore, when the insulation film 103 d is etched through a process of usual etching, i.e., reactive ion etching (RIE), the CVD oxide film 102 b and the thermal oxide film 102 d are not etched.

Further, because the film thickness of the thermal oxide film 102 d is larger than the film thickness of the insulation film 103 d, the film thickness of the interlayer insulation film 200A in the unit cell portion 11 becomes larger than the film thickness of the interlayer insulation film 300A in the termination region 12.

Therefore, exposure of the gate conductive film 2 a from the interlayer insulation film 200A due to etching can be reduced even when a local swelling occurs in the interlayer insulation film 200A in the unit cell portion 11 and the portion cannot be normally covered by a resist. Accordingly, occurrence of a leak failure between a gate and a source, which is caused due to exposure of the gate conductive film 2 a, can be reduced.

Note that, in the case of usual etching, i.e., RIE, etching including over-etching is performed. Therefore, regarding etching time or an etching amount, etching approximately 1.5 times as much as an actual film thickness of the CVD oxide film 103 b is performed.

Therefore, when an etching treatment including over-etching is taken into consideration, it is desirable that the film thickness of the thermal oxide film 102 d formed by thermal oxidation, i.e., cap oxidation, of the gate conductive film 2 a in the unit cell portion 11 be 0.5 times or more as large as the film thickness of the CVD oxide film 103 b.

FIG. 11 is a cross-sectional view schematically illustrating a cross-sectional structure of the termination region according to the embodiment. In FIG. 11, the gate contact region 3 c is formed in the interlayer insulation film 300A.

Next, the front-surface electrode 28 covering the source contact region 100 and the gate contact region 3 c is formed.

Effect Generated by Embodiment Described Above

Next, an effect generated by the embodiment described above will be illustrated. Note that the following description describes the effect based on a specific configuration illustrated in the embodiment described above. However, the specific configuration may be replaced by another specific configuration illustrated in the specification of the present application as long as a similar effect is generated.

According to the embodiment described above, in the method of manufacturing the semiconductor device, the gate oxide film 21 is formed on the upper surface of a semiconductor layer. Then, the gate conductive film 2 a to come in contact with the gate oxide film 21 is formed in the unit cell portion 11. Then, the gate wire 3 a to come in contact with the gate oxide film 21 is formed in the termination region 12. Then, a first insulation film is formed on the upper surface of the gate wire 3 a in the termination region 12. Then, the upper surface of the gate conductive film 2 a in the unit cell portion 11 is subjected to thermal oxidation with use of the first insulation film as a mask to form the thermal oxide film 102 d on the upper surface of the gate conductive film 2 a. Then, a second insulation film covering the first insulation film and the thermal oxide film 102 d is formed. Here, for example, the semiconductor layer corresponds to the n-type epitaxial layer 25. Further, for example, the first insulation film corresponds to the insulation film 103 d. Further, for example, the second insulation film covering the first insulation film corresponds to the CVD oxide film 103 b. Further, for example, the second insulation film covering the thermal oxide film 102 d corresponds to the CVD oxide film 102 b.

According to such a configuration, when the gate contact region 3 c is formed, exposure of the gate conductive film 2 a covered by the interlayer insulation film 200A in the unit cell portion 11 can be reduced even when a swelling locally occurs in the interlayer insulation film 200A in the unit cell portion. Specifically, after the insulation film 103 d is formed, the upper surface of the gate conductive film 2 a in the unit cell portion 11 is subjected to thermal oxidation with use of the insulation film 103 d as a mask to form the thermal oxide film 102 d on the upper surface of the gate conductive film 2 a. Accordingly, the film thickness of the thermal oxide film 102 d can be increased to be larger than the film thickness of the insulation film 103 d by adjusting a forming condition when the thermal oxide film 102 d is formed. Specifically, the film thickness of the interlayer insulation film 200A including the thermal oxide film 102 d can be increased to be larger than the film thickness of the interlayer insulation film 300A including the insulation film 103 d. Accordingly, exposure of the gate conductive film 2 a covered by the interlayer insulation film 200A can be reduced even if the interlayer insulation film 200A in the unit cell portion 11 is etched when the gate contact region 3 c is formed. Further, because the thermal oxide film 102 d is formed with use of the insulation film 103 d formed in the previous process as a mask, another mask need not be separately prepared to form the thermal oxide film 102 d.

Note that other configurations illustrated in the specification of the present application except these configurations may be omitted as appropriate. Specifically, provided that at least these configurations are included, the effect described above can be generated.

However, the effect described above can also be similarly generated when at least one of other configurations illustrated in the specification of the present application is added to the configuration described above as appropriate, i.e., when another configuration illustrated in the specification of the present application but not described as the configuration described above is added to the configuration described above.

Further, the order of performing each treatment may be changed as long as there is no limitation.

Further, according to the embodiment described above, the upper surface of the gate conductive film 2 a in the unit cell portion 11 is subjected to thermal oxidation with use of the first insulation film as a mask to form the thermal oxide film 102 d thicker than the first insulation film on the upper surface of the gate conductive film 2 a. Here, for example, the first insulation film corresponds to the insulation film 103 d. According to such a configuration, exposure of the gate conductive film 2 a covered by the interlayer insulation film 200A can be reduced even if the interlayer insulation film 200A in the unit cell portion 11 is etched when the gate contact region 3 c is formed.

Further, according to the embodiment described above, the second insulation film is an oxide film. Here, for example, the second insulation film covering the first insulation film corresponds to the CVD oxide film 103 b. Further, for example, the second insulation film covering the thermal oxide film 102 d corresponds to the CVD oxide film 102 b. According to such a configuration, exposure of the gate conductive film 2 a covered by the interlayer insulation film 200A can be reduced even if the interlayer insulation film 200A in the unit cell portion 11 is etched when the gate contact region 3 c is formed.

Further, according to the embodiment described above, the film thickness of the thermal oxide film 102 d is 0.5 times or more as large as the film thickness of the second insulation film. Here, for example, the second insulation film covering the first insulation film corresponds to the CVD oxide film 103 b. Further, for example, the second insulation film covering the thermal oxide film 102 d corresponds to the CVD oxide film 102 b. According to such a configuration, exposure of the gate conductive film 2 a covered by the interlayer insulation film 200A can be effectively reduced even if the CVD oxide film 103 b is subjected to an etching treatment including over-etching when the gate contact region 3 c is formed.

Further, according to the embodiment described above, in the unit cell portion 11, the source contact region 100 exposing the source implantation region 23 is formed. Then, the silicide 22 is formed in the source contact region 100. According to such a configuration, a gate contact is not opened when the silicide 22 is formed, and therefore the gate wire 3 a made of polysilicon or the like does not react with Ni at a high temperature.

Further, according to the embodiment described above, after the silicide 22 is formed in the unit cell portion 11, in the termination region 12, the gate contact region 3 c for exposing the gate wire 3 a is formed. According to such a configuration, a gate contact is not opened when the silicide 22 is formed, and therefore the gate wire 3 a made of polysilicon or the like does not react with Ni at a high temperature.

Further, according to the embodiment described above, the semiconductor layer is made of SiC. Here, for example, the semiconductor layer corresponds to the n-type epitaxial layer 25. According to such a configuration, exposure of the gate conductive film 2 a covered by the interlayer insulation film 200A can be reduced even if the interlayer insulation film 200A in the unit cell portion 11 is etched when the gate contact region 3 c is formed.

Further, according to the embodiment described above, the second insulation film covering the upper surface of the first insulation film and the side surface of the gate wire 3 a and the upper surface of the thermal oxide film 102 d and the side surface of the gate conductive film 2 a is formed. Here, for example, the first insulation film corresponds to the insulation film 103 d. Further, for example, the second insulation film covering the upper surface of the first insulation film and the side surface of the gate wire 3 a corresponds to the CVD oxide film 103 b. Further, for example, the second insulation film covering the upper surface of the thermal oxide film 102 d and the side surface of the gate conductive film 2 a corresponds to the CVD oxide film 102 b. According to such a configuration, exposure of the gate conductive film 2 a covered by the interlayer insulation film 200A can be reduced even if the interlayer insulation film 200A in the unit cell portion 11 is etched when the gate contact region 3 c is formed.

Further, according to the embodiment described above, the field oxide film 29 is formed on the upper surface of the semiconductor layer in the termination region 12. Then, in the termination region 12, the gate oxide film 21 is formed on the upper surface of the field oxide film 29. Here, for example, the semiconductor layer corresponds to the n-type epitaxial layer 25. According to such a configuration, exposure of the gate conductive film 2 a covered by the interlayer insulation film 200A can be reduced even if the interlayer insulation film 200A in the unit cell portion 11 is etched when the gate contact region 3 c is formed.

Modifications of Embodiment Described Above

While the embodiment described above may describe quality of a material, a material, a dimension, a shape, and a relative disposition relationship of each component, as well as a condition of implementation or the like, these are in all aspects illustrative and are not limited to the description of the specification of the present application.

Accordingly, unillustrated numerous modifications and equivalents are assumed within the scope of the technology disclosed in the specification of the present application. For example, a case of modifying, adding, or omitting at least one component is encompassed.

Further, a component described to be provided as “one” component in the embodiment described above may be provided as “one or more” components unless contradiction arises.

Further, each component in the embodiment described above is a conceptual unit. The scope of the technology disclosed in the specification of the present application encompasses a case in which one component is made of a plurality of structures, a case in which one component corresponds to a part of a certain structure, and a case in which a plurality of components are included in one structure.

Further, each component in the embodiment described above encompasses a structure having another structure or shape as long as the component exerts the same function.

Further, description in the specification of the present application is referred to for all of the purposes concerning the present technology, any of which is not to be admitted to be prior art.

Further, in the embodiment described above, when a name of a material is described without particular specification, another material, such as an alloy, which is obtained by adding another additive to the material, is encompassed unless contradiction arises.

Further, in the embodiment described above, the semiconductor substrate is an n type. However, the semiconductor substrate may be a p type. Specifically, the embodiment described above describes a MOSFET as an example of a silicon carbide semiconductor device. However, the embodiment described above may also assume a case in which an example of the silicon carbide semiconductor device is an insulated gate bipolar transistor (IGBT).

Note that, if an example of the silicon carbide semiconductor device is an IGBT, a source electrode corresponds to an emitter electrode, and a drain electrode corresponds to a collector electrode. Further, if an example of the silicon carbide semiconductor device is an IGBT, a layer having a conductivity type opposite to that of a drift layer is located on a lower surface of the drift layer. However, the layer located on the lower surface of the drift layer may be a layer newly formed on the lower surface of the drift layer, or may be a semiconductor substrate for the drift layer to be formed as in the embodiment described above.

Further, in the embodiment described above, the thermal oxide film 102 d is formed on the upper surface of the gate conductive film 2 a. However, the thermal oxide film 102 d may be formed also on the side surface of the gate conductive film 2 a, in addition to the upper surface of the gate conductive film 2 a. Further, the insulation film 103 d is formed on the upper surface of the gate wire 3 a. However, the insulation film 103 d may be formed also on the side surface of the gate wire 3 a, in addition to the upper surface of the gate wire 3 a.

Further, the embodiment described above describes a so-called vertical MOSFET. However, the embodiment described above may also assume a case in which a horizontal MOSFET is used.

Further, the embodiment described above describes a planar MOSFET. However, the embodiment described above may also assume a case in which a trench MOSFET, which has a trench formed on an upper surface of a drift layer, is used. In a case of the trench MOSFET, a groove portion, i.e., a trench, is formed on an upper surface of a drift layer, and a gate electrode is embedded on the upper surface of the drift layer in the groove portion, i.e., on a bottom surface of the trench, via a gate insulation film.

EXPLANATION OF REFERENCE SIGNS

2 a gate conductive film, 2 b, 3 b, 102 b, 103 b CVD oxide film, 2 d, 3 d, 102 d thermal oxide film, 3 a gate wire, 3 c gate contact region, 11 unit cell portion, 12 termination region, 21 gate oxide film, 22 silicide, 23 source implantation region, 24 well implantation region, 25 epitaxial layer, 26 SiC semiconductor substrate, 27 back-surface electrode, 28 front-surface electrode, 29 field oxide film, 100 source contact region, 103 d insulation film, 200, 200A, 300, 300A interlayer insulation film 

The invention claimed is:
 1. A method of manufacturing a semiconductor device, the method comprising: forming a gate oxide film on an upper surface of a semiconductor layer; forming a gate conductive film to come in contact with the gate oxide film in a unit cell portion; forming a gate wire to come in contact with the gate oxide film in a termination region provided to surround the unit cell portion in plan view; forming a first insulation film on an upper surface of the gate wire in the termination region; subjecting an upper surface of the gate conductive film in the unit cell portion to thermal oxidation with use of the first insulation film as a mask to form a thermal oxide film on the upper surface of the gate conductive film; and forming a second insulation film covering the first insulation film and the thermal oxide film.
 2. The method of manufacturing a semiconductor device according to claim 1, wherein the second insulation film is an oxide film.
 3. The method of manufacturing a semiconductor device according to claim 1, wherein a film thickness of the thermal oxide film is 0.5 times or more as large as a film thickness of the second insulation film.
 4. The method of manufacturing a semiconductor device according to claim 1, wherein a source contact region is formed in the unit cell portion, and a silicide is formed in the source contact region.
 5. The method of manufacturing a semiconductor device according to claim 4, wherein after the silicide is formed in the unit cell portion, a gate contact region is formed in the termination region.
 6. The method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor layer is made of SiC.
 7. The method of manufacturing a semiconductor device according to claim 1, wherein the second insulation film covering an upper surface of the first insulation film and a side surface of the gate wire, and an upper surface of the thermal oxide film and a side surface of the gate conductive film is formed.
 8. The method of manufacturing a semiconductor device according to claim 1, wherein a field oxide film is formed on the upper surface of the semiconductor layer in the termination region, and the gate oxide film is formed on an upper surface of the field oxide film in the termination region.
 9. The method of manufacturing a semiconductor device according to claim 1, wherein the thermal oxide film is formed also on a side surface of the gate conductive film, in addition to the upper surface of the gate conductive film. 